Heat Engines and Refrigerators

Which of the following statements is correct, in case of adiabatic expansion?

A frictionless heat engine can be $100\%$ efficient only if its exhaust temperature is

A polyatomic gas has $3$ translational, $3$ rotational degrees of freedom and $2$ vibrational modes. What is molar specific heat ratio for the gas?

The efficiency is always

A refrigerator with a $50\mathrm{W}$ motor is to be used to freeze $2\mathrm{kg}$ of water at $273\mathrm{K}$ in an insulated vessel. The outside temperature is $300\mathrm{K}$. The smallest possible time to do this is (take the latent heat of fusion of water to be $3.33\times {10}^5 \mathrm{J}·{\mathrm{kg}}^{-1}$)

Which device maintains a body at a temperature lower than the temperature of the surroundings?

When the state changes from $\mathrm{A}$ to $\mathrm{B}$. What will happens to internal energy?

The internal energy of compressed real gas, as compared to that of the ideal gas at the same temperature is

The internal energy during the free expansion process

A diatomic ideal gas is used in a carnot engine as the working substance. If during the adiabatic expansion part of the cycle, the volume of the gas increases from $V$ to $32 \mathrm{V}$, the efficiency of the engine is,

The internal energy of a gas during isothermal expansion

The internal energy of a prefect gas does not change during 

The thermodynamic process in which the pressure of the system remains contant is called 

Two identical samples of gas are allowed to expand $\left(\mathrm{i}\right)$ isothermally and $\left(\mathrm{ii}\right)$ adiabatically. The amount of work done id then

Compressed air coming out of punctured football becomes cooler because of

A Carnot engine works between constant temperature $T_1$ and $T_2$ of source and sink, respectively. For efficiency to be greatest

In the free expansion of an Ideal gas, its internal energy

In a non cyclic process, which of the following statement is correct?

Quasi-static process is : 

The internal energy of compressed real gas as compared to that of the ideal gas at the same temperature is: